Apparatus and method for stereotactic surgery

ABSTRACT

The trajectory of a surgical instrument or tool used for a stereotactic medical procedure is controlled by a passive apparatus having two pivots into which the tool may be inserted. The pivots, which serve as end effectors, are placed at points along a selected trajectory. The pivots are mounted to members attached to carriages. The carriages allow movement in a plane, whereas the members may move perpendicular to the plane. Indicia allow the pivots to be moved to a desired point and fasteners then secure the pivots in place, while allowing the pivots free rotation relative to two perpendicular axes.

CROSS REFERENCE TO RELATED APPLICATION

This application relates to copending application Ser. No. 07/883,736filed concurrently herewith and assigned to the same assignee as thepresent invention.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for trajectory supportof a surgical tool during an imaging-guided surgical operation.

Stereotactic frames play an important part in stereotactic surgery. Suchframes provide a means to define a mechanical or physical trajectory inthree dimensions and to support a surgical instrument or tool such thatit may reach a target along the trajectory. For example, a patient mayhave a brain tumor which should be removed or otherwise treated. Animaging system such as computerized tomography allows the surgeon toprecisely define the location of the tumor or other target. The surgeonselects an incision point on the skull of the patient and the locationof the incision point is relatively precisely identified. The trajectorywhich the surgical tool or instrument should use is defined by thetarget and incision. Various stereotactic frames have been used toinsure that the surgical tool follows the planned trajectory.

Since much of the activity in stereotactic surgery has been related toneurosurgery, targets are usually considered points inside a sphere,whereas incision points are selected from the surface of the sphere.Accordingly, the frames have been designed to work in a partly enclosedspace such as the human head. Setting up of such an apparatus usuallyinvolves setting a number of rotational angles. For example, the mostpopular BRW frame uses four angles. Given the target and incisionpoints, a special program determines four angles. As shown in FIG. 1,the prior art BRW frame 10 allows placement of a needle 12 within apatient. The frame 10 supports the needle 12 in its trajectory. Becausethe frame uses a non-intuitive coordinate system, a surgeon often has torepeat the calculations several times to make sure that the set ofangles are correct. Further, the calculations are non-linear and thenon-linearity may introduce positional errors.

Since stereotactic surgery is usually much less invasive than normalsurgery, it is becoming more popular for surgical operations beyondtraditional stereotactic neurosurgery. The usefulness of stereotacticsurgery for operating on the neck, spine, and abdomen is becoming moreappreciated. In those operations, mechanical support without a framebecomes essential. Typically, a frameless support system would use arobotic arm. Given a target and incision pair based upon apreoperatively acquired three dimensional image set and a patient spaceto image space registration scheme, a robot arm can be programmed toprovide a trajectory support for the surgical instrument.

FIG. 2 shows a prior art robotic arm arrangement developed by Kwoh. Theidea is that the patient is imaged in the same reference system as therobot arm sits. Once the target and incision pair is determined, thecomputer that drives the arm can be instructed to orient an end effector14 to such a position that a surgical tool can be held by the assemblyand extended to touch the target inside the patient. The arm in thisdesign is active which, when instructed, does the orientation itself.Furthermore, it can be instructed to aim the end effector at the targetas the trajectory is being changed. This feature allows the surgeon toexplore all the possible incision points. This arrangement is describedin more detail in Y. S. Kwoh, "A New Computerized Tomographic-AidedRobotic Stereotaxis System", Robotics Age, 7(6):17-21(1985).

A prior art passive arm is shown in FIG. 3. This design allows thesurgeon to move an end effector 6 around and, correspondingly, theposition of the end effector is displayed in the context of the threedimensional image acquired preoperatively. This design enables thesurgeon to explore possible trajectories with total freedom. Moredetails about this design may be obtained from Y. Kosugi et al., "AnArticulated Neurosurgical Navigation System Using MRI and CT Images",IEEE Transactions on Biomedical Engineering, 35(2):147-151(1988).

Among problems with robot assisted and other frameless support systemsare design complexities. Such robotic designs often leave little controlto the surgeon. Furthermore, the sophisticated and expensive positionalfeedback systems are unnecessary when one is within imaging-guidedsurgical procedures. That is the imaging process can be used to trackthe position of the instrument or tool such that calculations of suchinformation indirectly from the positional information of all the jointsof the robot arm is not required.

OBJECTS AND SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to providea new and improved stereotactic trajectory support apparatus and method.

A more specific object of the present invention is to providestereotactic trajectory support using a relatively simple andinexpensive design.

A further object of the present invention is to provide stereotactictrajectory support which is relatively convenient and user-friendly.

A further object of the present invention is to provide stereotactictrajectory support without requiring use of a non-intuitive coordinatesystem and/or without requiring non-linear calculations.

The above and other objects of the present invention are realized by astereotactic trajectory apparatus having a support structure and firstand second surgical tool holders supported by the support structure. Thesurgical tool holders are independently movable relative to the supportstructure to positions corresponding to different x, y, z coordinates,the x, y, z coordinates corresponding respectively to orthogonal x, y,and z axes. The first and second surgical tool holders are respectivelyfirst and second pivots. Each pivot defines a point on a surgical tooltrajectory. Each pivot is rotatable about perpendicular first and secondpivot axes without changing the x, y, z coordinates of the correspondingpoint. The first pivot axis of each pivot is perpendicular to an xzplane in which the x and z axes extend and the second pivot axis of eachpivot is parallel to the xz plane.

First and second members are movably attached respectively tocorresponding first and second carriages. Each carriage is supported bythe support structure for movement in a plane perpendicular to alengthwise direction of the corresponding member. The first and secondmembers extend lengthwise in parallel and the first and second carriagesare mounted for movement in tracks on the support structure.

The support structure further includes parallel first and secondcarriages tracks extending along the z axis in which the first andsecond carriages move and each of the first and second carriage tracksis movable along the x axis. The support structure further includes an xtrack extending along the x axis and in which each of the first andsecond carriage tracks is movable. Fasteners allow selective fixing ofthe first and second carriages respectively to the first and secondcarriage tracks. Other fasteners allow selective fixing of the first andsecond carriage tracks to the x track. Still further fasteners allowselective fixing of the first and second members respectively to thefirst and second carriages. Indicia indicative of the x, y, zcoordinates of the points defined by the first and second pivots arelocated on the support structure and/or the members.

Each of the pivots is always freely movable about its first and secondpivot axes unless a surgical tool is disposed within the pivot. In otherwords, the trajectory apparatus does not have any means for locking thepivots against movement in their first and second pivot axes.

Advantageously, the apparatus is passive.

The method of the present invention includes identifying a target P₀ andincision pint P₁ for performing a medical stereotactic procedure. Atrajectory path having P₀ and P₁ thereon is determined for a surgicaltool. Independently movable first and second pivots are securedrespectively at points P₂ and P₃ on the trajectory path. Points P₂ andP₃ are determined by positioning the first and second pivots usingindicia linearly related to x, y, z coordinates corresponding toorthogonal x, y, z axes. Each of the first and second pivots isrotatable about perpendicular first and second pivot axes withoutchanging the x, y, z coordinates of the corresponding respective one ofpoints P₂ and P₃. Next, a surgical tool is placed through the first andsecond pivots to extend along the trajectory path to within the patient.

Before the securing step, first and second carriages are moved topositions corresponding to the x, z coordinates respectively of P₂ andP₃, and first and second members, which are movably mounted respectivelyto the first and second carriages, are moved to locations such thatfirst and second pivots mounted respectively thereon are at the ycoordinates respectively of P₂ and P₃. The first and second carriagesmoved in an xz plane in which the x axis and z axis are disposed bymovement along tracks. The securing step includes securing the first andsecond carriages and securing the first and second members.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will be morereadily understood when the following detailed description is consideredin conjunction with the accompanying drawings wherein like charactersrepresent like parts throughout the several views and in which:

FIG. 1 is a simplified perspective view of a patient having a prior artstereotactic frame attached to him as discussed above;

FIG. 2 shows a perspective of a patient having surgery using a prior artrobotic arm as discussed above;

FIG. 3 shows a prior art passive arm system for operating on a patientas discussed above;

FIG. 4 is a simplified perspective illustration of the concept of thepresent invention;

FIG. 5 is an end view of a structure used to implement the concept ofFIG. 4;

FIG. 6 is a view of a part of FIG. 5 from the side;

FIG. 7 is a perspective view of a part of the structure of FIG. 5;

FIG. 8 is a cross section view of a part of the structure of FIG. 5;

FIG. 9 is a perspective view with parts broken away and a portion incross section of a part of the FIG. 5 structure; and

FIG. 10 is cross section view of a pivot;

FIG. 11 is a cross section view taken along lines 11--11 of FIG. 10 andincluding lines 10--10 corresponding to the view of FIG. 10; and

FIG. 12 is a graphic illustrating a range of trajectories.

DETAILED DESCRIPTION

The principle of the operation of the present invention will bediscussed with reference to FIG. 4 in which points P₀ and P₁respectively are the target and incision point within a patient. Thetarget and incision point would be determined using known techniques asdiscussed above. Specifically, an imaging system allows the surgeon toselect the target P₀ which has coordinates (X₀, Y₀, Z₀). The incisionpoint P₁ having coordinates (X₁, Y₁, Z₁) is selected so that the twopoints P₀ and P₁ define a trajectory 18. For the usual case in which thetrajectory 18 is a line, the line can be written as: ##EQU1## where α=X₁-X₀, b=Y₁ -Y₀, and c=Z₁ -Z₀,. Using the two equations, two points P₂=(X₂,Y₂,Z₂) and P₃ =(X₃,Y₃,Z₃) can be selected which lie on the sametrajectory line 18 defined by points P₀ and P₁. A typical way to makethe selection would be to pick two heights Y₂ and Y₃ and then use theequations 1 and 2 to calculate the X and Z values for those points. Oncethe coordinates for the points P₂ and P₃ are determined, apparatus 20 ofthe present invention would be used. Specifically, the apparatus 20 is astereotactic trajectory apparatus having a support structure 22 havingfirst and second pivots 24F and 24S respectively supported thereby. Aswill be discussed in more detail below, the pivots 24F and 24S may besleeves, rings, or other shapes adapted to receive a surgical tool, suchas a needle, such that two of the pivots made together hold the needlealong a trajectory path such as the line 18. The first and second pivotsare respectively mounted to first and second members 26F and 26S, whichis turn are secured in respective first and second carriages 28F and28S. Carriages 28F and 28S move along support structure 22 in the xzplane. More specifically, carriages 28F and 28S travel alongcorresponding first and second z tracks 30F and 30S. The tracks 30F and30S move in the x direction by track movement along two parallel xtracks 32.

Although not shown in the schematic of FIG. 4, indicia would be includedon the support structure 22 and the members 26F and 26S so that thepivots 24F and 24S could be precisely placed at points P₂ and P₃.Additionally, indicia may be included on the surgical tool, such asneedle (not shown) which would be inserted in pivot 24S and alongtrajectory line 18 so that, by knowing the distance from P₃ to P₀, thesurgeon can insert the needle or other tool within pivot 24S only as faras necessary so that the tip of the needle would reach P₀.

Turning now to FIG. 5, the trajectory apparatus 20 of the presentinvention is shown attached to an operating table 34 upon which apatient is secured. The apparatus 20 is shown secured to portion 34S oftable 34 by a thumb screw 34T at one corner of the base 22 of apparatus20. However, in actual practice, four such thumb screws or otherfasteners may be used at each of four corners of the generallyrectangular base 22. Each of the thumb screws would extend through ahole in part of the base 22 and into corresponding holes in parts of thetable 34. More specifically, the thumb screws could extend through holesin the two identical x tracks 32 (only one of which is visible in FIG.5). The table 34 includes a cut-out portion 34C, which may be arectangular cut-out section corresponding in shape to the base 22 andbeing slightly smaller in size than the base 22. The cutout sectionallows members 26F and 26S to be moved vertically (i.e., along the yaxis) relative to their respective first and second carriages 28F and28S.

Continuing to view FIG. 5, but also considering FIG. 6, it will be seenthat the track 30F moves along opposite side tracks 32 (only one isvisible in FIGS. 5 and 6) by use of a wedge portion 36 sliding in amating channel or slot 38. An arrangement such as thumb screw 40extending through a hole in track 30F and pressing against the topsurface of track 32 or some other fastener arrangement may be used tosecure track 30F relative to track 32, while still allowing movement oftrack 30F relative to track 32 when such movement is desired in order toplace pivot 24F in its proper position. Although only one end of thetrack 30F is shown in FIG. 6, it will be appreciated that the oppositeend of the track 30F would be constructed in identical fashion and wouldslide in the other track 32.

With reference now to FIG. 7, the track 30F may have a mark 42 disposedon its end, which mark lines up with different indicia 44 on track 32,the indicia 44 having numerals (not shown) such that the x coordinate ofthe pivot 24F may be read from the indicia 44.

With reference now to FIGS. 7-9, the track 30F has a wedge-shapedchannel 46 in which the carriage 28F may slide. The bottom of channel 46in which the carriage 28F may slide, has a cut-out slot 48 extendingsubstantially along the length of channel 46 so that the member 26F mayextend through a hole (not separately labeled) in carriage 28F. Themember 26F is moved up and down so that the pivot 24F is disposed at theproper y coordinate whereupon a thumb screw 50 is used to fix it inposition relative to carriage 28F. The thumb screw 50 may, as with theother thumb screws discussed herein, be replaced by other fastenerelements.

Indicia 52 on member 26F may be read (as by lining up to the top ofcarriage 28F) to determine the y coordinate of the pivot 24F. As withthe other indicia discussed, indicia 52 may have numbers (not shown)associated with indication marks and would extend substantiallycompletely over the range of relative movement even though only a fewindicia are shown in the figures.

The carriage 28F may have a flange 54 so that thumbscrew 56 (FIGS. 5 and8) may lock the carriage against movement in the same fashion asdiscussed with respect to thumbscrew 40.

Indicia 58 (FIG. 8 only) are disposed on the top of track 30F to allowcarriage 28F to be placed such that pivot 24F has the proper zcoordinate. As with the other indicia, a marker, pointer, or part of thecarriage 28F may line up with the indicia to allow reading thereof.

The member 26S, carriage 28S, and carriage (i.e., carriageaccommodating) track 30S are respectively identical to member 26F,carriage 28F, and track 30F.

The arrangement of FIG. 5 gives the pivots 4F and 24S three degrees offreedom corresponding to the x, y, and z axes, which are threeorthogonal axes. As used herein, the x, y, and z axes would notnecessarily have the shown orientation with x anc z axes beinghorizontal and the y axis being vertical. Although the support structure22 made of tracks 30F, 30S, and 32 is shown horizontal, attached to thetable 34, and beside the patient in FIG. 5, other orientations andmounting arrangements might be used. The structure 22 could be suspendedfrom the ceiling of the operating room with the pivots 24F and 24Sdisposed below the structure 22. The apparatus 20 might alternately bemounted so that structure 22 was vertical and members 26F and 26Sextended horizontally. Regardless of the orientation and placement ofthe trajectory apparatus 20, the indicia on the apparatus should givecoordinates relative to the patient frame of reference, either directlyor by use of a simple linear transformation.

Turning now to FIGS. 10 and 11, the construction of pivot 24F will bediscussed. (Pivot 24S is identical to pivot 24F.) Pivot 24F is shown asa sleeve, although it could alternately be a ring, loop, partial ring,or other shape allowing it to receive a surgical tool, such as a needle,directly or indirectly (e.g., needle holder or cannula fits in pivot andin turn holds needle within pivot). Pivot 24F is mounted to yoke 60 forpivoting about pivot axis 62. Yoke 60 is in turn mounted to member 26Ffor rotation about pivot axis 64.

Once the pivots 24F and 24S are placed at points P₂ and P₃, the surgeonpasses the tip of a surgical tool 66 (partially shown only in FIG. 5)through pivot 24S and towards pivot 24F. The pivots 24F and 24S are endeffectors which orient themselves by assuming the proper angles (i.e.,no need to set an angle explicitly) by pivoting about their two pivotaxes as the tool 66 goes into pivot 24F. The tool will be constrained tofollow trajectory path 18 and the surgeon would insert it to thepreviously determined depth so that the tip of tool 66 reaches thetarget.

As a check on the linear calculations (i.e., equations 1 and 2 above)and the settings actually used for placement of pivots 24F and 24S, athird pivot 24T and third member 26T (FIG. 5 only) might be placed at apoint P₄ by applying the techniques used for the other pivots. If therewas a calculation mistake or mistake in positioning the three pivots,the identical pivots 24F, 24S, and 24T would not line up and wouldprevent the tool 66 from being applied to the patient. The member 26T isonly partially shown in FIG. 5 and would be securable to a carriage andtrack (not shown) in the same fashion as member 26F.

Al alternate way of checking the settings on apparatus 20 would involveusing a phantom to establish simulated target and incision points asdescribed in the above mentioned present inventor's U.S. applicationSer. No. 07/883,736 (RD-21255), filed concurrently herewith, entitled"METHOD AND APPARATUS FOR STEREOTACTIC TRAJECTORY SPECIFICATION",assigned to the assignee of the present application and herebyincorporated by reference. That application uses a phantom which issimilar to some respects to apparatus 20.

The apparatus 20, or parts of it, may be made of non-ferromagneticmaterials such as carbon fiber for applications in magnetic resonanceimaging-guided surgeries.

FIG. 12 shows the head 68H of a patient to illustrate that trajectorieswithin cones 68C corresponding to incision points at surface area 68Scould not be used with the present invention as carriages 28F and 28Scould not be disposed at the same or too close x coordinates. The sizeof the cones could be minimized by making tracks 30F and 30S as narrowas possible or otherwise optimizing the design of the tracks and/or thepivots. In ordinary situations, the patient can be repositioned if theproposed trajectory falls within one of the cones. If desired, thetracks 30F and 30S could be mounted to slide in different, verticallyoffset x tracks so as to improve the range of allowable trajectories.

Although various specific constructions have been described herein, itis to be understood that these are for illustrative purposes only.Various modifications and adaptations will be apparent to those of skillin the art. Accordingly, the scope of the present invention should bedetermined by reference to the claims appended hereto.

What is claimed is:
 1. A stereotactic trajectory apparatus comprising:asupport structure; and first and second surgical tool holders supportedby said support structure and independently movable relative to saidsupport structure to positions corresponding to different x, y, zcoordinates, the x, y, z coordinates corresponding respectively toorthogonal x, y, and z axes, wherein said first and second surgical toolholders are respectively first and second pivots, each pivot defining apoint on a surgical tool trajectory, and wherein each pivot is rotatableabout perpendicular first and second pivot axes without changing the x,y, z coordinates of the corresponding point.
 2. The stereotactictrajectory apparatus of claim 1 wherein said first pivot axis of eachpivot is perpendicular to an xz plane in which the x and z axes extendand said second pivot axis of each pivot is parallel to the xz plane. 3.The stereotactic trajectory apparatus of claim 2 further comprisingfirst and second members each having top and bottom portions, saidmembers being movably attached respectively to corresponding first andsecond carriages at their bottom portions, and to said first and secondsurgical tool holders at their top portions, each carriage beingsupported by the support structure for movement in a plane perpendicularto the lengthwise direction of the corresponding member.
 4. Thestereotactic trajectory apparatus of claim 3 wherein said first andsecond members extend lengthwise in parallel and said first and secondcarriages are mounted for movement in tracks on said support structure.5. The stereotactic trajectory apparatus of claim 4 wherein said tracksof said support structure further comprises parallel first and secondcarriage tracks extending along the z axis in which said first andsecond carriages move and each of said first and second carriage tracksis movable along the x axis.
 6. The stereotactic trajectory apparatus ofclaim 5 wherein said tracks of said further comprises an x trackextending along the x axis and in which each of said first and secondcarriage tracks is movable.
 7. The stereotactic trajectory apparatus ofclaim 6 wherein said support structure further comprises fasteners forselectively fixing said first and second carriages respectively to saidfirst and second carriage tracks, fasteners for selectively fixing saidfirst and second carriage tracks to said x track, and fasteners forselectively fixing said first and second members respectively to saidfirst and second carriages.
 8. The stereotactic trajectory apparatus ofclaim 7 further comprising indicia of said support structure indicativeof the x, y, z coordinates of said points defined by said first andsecond pivots.
 9. The stereotactic trajectory apparatus of claim 5wherein each of said pivots is always freely movably about its first andsecond pivot axes unless a surgical tool is disposed within the pivot.10. The stereotactic trajectory apparatus of claim 1 wherein each ofsaid pivots is always freely movably about its first and second pivotaxes unless a surgical tool is disposed within the pivot.
 11. Thestereotactic trajectory apparatus of claim 1 further comprising indiciaon said support structure the x, y, z coordinates of said points definedby said first and second pivots.
 12. The stereotactic trajectoryapparatus of claim 1 further comprising a third surgical tool holdersupported by said support structure and movable independently of saidfirst and second surgical tool holders to positions corresponding todifferent x, y, z coordinates, and wherein said third surgical toolholder is a third pivot defining a point on a surgical tool trajectoryand is rotatable about perpendicular first and second pivot axes withoutchanging the x, y, z coordinates of the corresponding points.
 13. Amethod comprising the steps of:identifying a target P₀ and incisionpoint P₁ for performing a medical stereotactic procedure; determining atrajectory having P₀ and P₁ thereon for a surgical tool; securingindependently movable first and second pivots respectively at points P₂and P₃ on the trajectory, points P₂ and P₃ determined by positioning thefirst and second pivots using indicia linearly related to x, y, zcoordinates corresponding to orthogonal x, y, z axes, each of the firstand second pivots being rotatable about perpendicular first and secondpivot axes without changing the x, y, z coordinates of the correspondingrespective one of points P₂ and P₃ ; and placing a surgical tool throughthe first and second pivots to extend along the trajectory to within thepatient.
 14. The method of claim 13 further comprising the steps of,before the securing step:moving first and second carriages to positionscorresponding to the x, z coordinates respectively of P₂ and P₃ ; andmoving first and second members movably mounted respectively to saidfirst and second carriages to locations such that the first and secondpivots mounted respectively thereon are at the y coordinatesrespectively of P₂ and P₃.
 15. The method of claim 14, wherein the firstand second carriages are moved in an xz plane, in which the x and z axesare disposed, by movement along tracks.
 16. The method of claim 14wherein the securing step includes securing the first and secondcarriages and securing the first and second members.
 17. The method ofclaim 13 further comprising: securing an independently movable thirdpivot at point P₄ on the trajectory, point P₄ determined by positioningthe third pivot using the indicia, the third pivot being rotatable aboutperpendicular first and second pivot axes associated with the thirdpivot and without changing the x, y, z coordinates of point P₄ ; andplacing a surgical tool through the third pivot, as well as the firstand second pivots, to extend along the trajectory to within the patient.